The T lymphocyte activation scheme is set in motion by the interaction of processed antigen in context of MHC products with the T lymphocyte receptor for nominal antigen which is closely associated with the pan T cell antigen, T3 (Leu-4, CD3). Antibodies directed against either the T cell receptor or T3 mimic antigen and lead to changes consistent with the activated state. This activation appears to be dependent upon the phospholipase C- catalyzed generation of the second messengers, inositol 1, 4, 5- trisphosphate and diacylglycerol. Inositol trisphosphate increases intracellular calcium concentration by releasing Ca++ from intracellular stores while diacylglycerol activates protein kinase C. We recently have shown that other inositol polyphosphates, particularly inositol tetrakisphosphate and inositol 1, 3, 4- trisphosphate, are produced as a consequence of perturbation of the T cell receptor-T3 complex. In this proposal, we outline a series of experiments designed to investigate the molecular mechanisms which control inositol polyphosphate formation in T lymphocytes following stimulation of the T cell receptor-T3 complex. We will investigate control of antigenic signal transduction by guanine nucleotide-binding regulatory proteins. These G-proteins, which regulate adenylate cyclase activity, recently have been implicated in control of phospholipase C activity as well. We shall investigate the regulatory roles of eicosanoids, particularly PGE2, and the well defined pan T cell surface antigen, T1, in the early events of T lymphocyte activation. Finally, we shall attempt to implicate inositol phosphate production as a mechanism of T lymphocyte activation by oxidants. Using the techniques of cellular electrophysiology, we will explore ion channel events in T lymphocyte activation including the possibility of inositol tetrakisphosphate or inositol 1, 3, 4-trisphosphate control of K+ or Ca++ ion channel activity. These studies should significantly improve our understanding of the phenomenon of T lymphocyte activation and have broad implications for control of immunological events and cellular proliferation including neoplasia.